Environmental pollution is a problem adversely affecting the planet and its inhabitants. Fortunately, a majority of the individuals recognize the necessity of reducing the emission of greenhouse gases and the necessity of protecting our oceans.
One large source of pollution is maritime vessels, by virtue of the fact that the oceans cover a majority of the planet and there is a lot of maritime vehicle traffic. There are a number of conventional technologies that are designed to try to control the air pollution caused by combustion and water pollution associated with ballast water that is associated with maritime vessels, but it remains to be seen whether any of those technologies can successfully mitigate that pollution.
The International Maritime Organization (IMO) provides guidance and regulation for maritime vessels worldwide. There are three main areas identified by IMO as being the most destructive to our environment: exhaust sulfur dioxide (SO2), exhaust oxides of nitrogen (NOx), and ballast water pollution associated with aquatic organisms.
Various literature discusses that seawater may be useful method for removing most of the SO2 generated in combustion devices aboard vessels. Unfortunately, there are few published scientific studies addressing the removal efficiencies of seawater SO2 scrubbers.
One study from Italy by G. Caiazzo (G. Caiazzo—Seawater SO2 scrubbing in a tower for marine applications-Universita degli Studi di Napoli Federico II, Via Claudio 21, Napoli 80125, Italy) evaluates SO2 removal efficiency base research that compares seawater scrubber residence time, liquid flow rate and SO2 concentration. His findings show a maximum removal efficiency of 93% with a 3.4 second reaction residence time and a liquid to gas ratio of 0.01 to 1. This is a long residence time that will require a large scrubber vessel and an enormous amount of seawater flow through a full-scale device. It is noteworthy that the reported removal efficiency will not meet 2016 and 2020 International Maritime Organization (IMO) rules for SO2 emissions when the vessel is using conventional fuels with 3.5% sulfur content. Those operating marine vessels will have to make a decision between using more expensive fuels and paying for combustion device upgrades to accommodate the low sulfur fuels or adding an additional SO2 abatement device.
Most of the papers and patents that describe seawater treatments for SO2 or SOx describe coarse spray devices or countercurrent scrubbers. CA1303822 discloses improved SO2 adsorption by recirculating aqueous stream of sea water containing magnesium hydroxide and magnesium sulfite in a countercurrent packed bed scrubber.
Statoil's refinery at Mongstad, Norway has been using a seawater flue gas desulfurization unit that has a countercurrent packed bed scrubber. (See http://www.ogj.com/articles/print/volume-89/issue-26/in-this-issue/refining/seawater-scrubbing-removes-so2-from-refinery-flue-gases.html)
WO 1992008541 claims SO2 and NOx abatement in a two-stage process that involves spray of seawater into ducting that precedes the first stage. The first stage apparently bubbles the exhaust gas into a pool of seawater for SO2 abatement. The second stage NOx treatment is done in a packed bed scrubber that adds urea (NH2)2CO to seawater at ambient temperatures. The patent application does not clearly identify the packing material in the NOx scrubber and there is no mention of a catalyst.
EP 3132839 describes a two-stage packed bed scrubber using seawater that has been pH adjusted by the addition of an alkaline material. There is no disclosure of removal efficiency.
There are several patents and patent publications directed to marine NOx abatement using SCR technology. None were found for marine NOx abatement using (ClO2)0. Some patents for selective catalytic reduction or “SCR” technology report removal efficiencies between 85% and 93%. These also incorporate soot blowers to clean off the catalyst beds. CN101922333B candidly identified the challenges associated with SCR catalyst poisoning and clogging associated with processing exhaust generated from high sulfur marine fuels. The concerns include: a) SCR catalyst can be poisoned by sulfur fuels; b) marine engine operating conditions change frequently—at low load conditions the exhaust temperature is too low to effectively utilize the SCR technology; and c) for safety reasons ships are unable to use ammonia and are required to use 40% aqueous urea which has supply and cost considerations. The patent clearly specified the reported technology is only applicable to marine fuels with less than 1.5% sulfur.
Particulate and particulate matter are also broadly recognized in scientific literature as a source of health issues. Environmental agencies in many countries have imposed regulatory requirements for particulate emissions from diesel engines and other sources. As will be discussed herein, diesel fuel exhaust has additional issues that require special consideration from a chemical treatment perspective. O. Sippula paper: Particle Emissions from Marine Engines: Chemical Composition and Aromatic Emission Profiles under Various Operating Conditions, 2014, American Chemical Society, provides comprehensive data describing the particles. Other scientific papers characterize particulate by particle number and particle mass. Literature teaches that most particles produced by combustion process in diesel engines are sized between 3 nm to 1 μm in diameter. The particles are distinguished by their distribution characteristic often described as “nucleation and accumulation”. Particles below 30-50 nm in diameter are normally in the “nucleation” mode. By definition nucleation is the first step in the formation of either a new thermodynamic phase or new structure via self-assembly or self-organization. This group has less than 20% of the total particulate mass and up to 95% of the total number of particles. The second mode is call “accumulation” and it usually consists of particles ranging between 50 and 150 nm in diameter. This group contains most of the particle mass and lower particle count, and comprises agglomerated solid carbon particles together with associated absorbed heavy hydrocarbons as described in the previously mentioned paper by Sippula.
Regulatory requirements address particulate formation through restriction of sulfur content in marine fuels and via other means of regulatory compliance. However, in the Ushakov paper entitled: “Effects of High Sulphur Content in Marine Fuels on Particulate Matter Emission Characteristics”; Journal of Marine Engineering and Technology (2013), the reduction of fuel sulphur content to zero will not alone eliminate the problem of particulate matter emissions, since particulates and particulate matter are made up of a wide variety of components such as carbonaceous fractions, sulphates and water, partially burned fuel and lubrication oil, etc. Lowering fuel sulfur content thus has only limited potential in terms of particulate or particulate matter control.
To this end, it would be desirable to provide methods and related apparatus that can address exhaust contamination with various contaminants, including SOx and sulfur dioxide (SO2), exhaust oxides of nitrogen (NOx), organic compounds, and particulates or particulate matter; and can address ballast water pollution associated with aquatic organisms that includes: a) a process that can be stand-alone addressing just exhaust gas or can be included with other abatement technologies such as ballast water treatment, wastewater treatment, drinking water treatment, and habitable space air treatment, b) serves the marine industry and other industries that utilize or have access to seawater, c) has relatively high removal efficiencies of SOx and sulfur dioxide (SO2), exhaust oxides of nitrogen (NOx), organic compounds, and particulates or particulate matter, as compared with conventional technologies, d) has a relatively low overall operating cost, as compared with conventional technologies; and e) utilizes non-ionic chlorine dioxide (ClO2)0 to accomplish these environmental services in whole or in part, and therefore, reduces equipment cost by cross-utilizing the facilities necessary to generate and regulate the production of (ClO2)0.